An exploratory development model was designed, constructed and evaluated. The design followed the criterion set forth in efficiency improvements in Coupled Cavity TWTs with the exception of a confined flow beam instead of brilluoin focusing. The results exceeded all performance parameters except interaction efficiency. Electronic efficiency, however was found to be 45% with 33% depression of a standard single stage collector. The measured interaction efficiency agreed well with predicted efficiency. Bandwidth of 500 MHz with .5db maximum variation was displayed and very low ripple in both amplitude and phase. Tube stability was excellent.